In some situations it is desirable to electrically isolate two circuits from each other while enabling the circuits to communicate. This may be done for isolating the circuits' grounds from each other, or for reducing the coupling of noise from one circuit to the other, or for any other purpose. Common techniques used for such “galvanic isolation” include using transformers or optical links.
Transformers tend to be relatively large and expensive. Optical links require an LED and a photodetector, which add significant size and cost to the circuits. Optical links are not susceptible to electromagnetic interference (EMI), but the electronics in the photodiode detector circuit are susceptible to EMI. Shielding of connectors may be used to mitigate the effects of ambient EMI, and internal EMI shielding may be added to the package, but such shielding adds cost. Filters to filter out the EMI may be added to the receiver but add signal delay.
What is needed is a more compact and inexpensive technique to galvanically isolate two or more circuits, such as separate dies within an integrated circuit (IC) package, or separate circuits on a printed circuit board (PCB), that communicate with each other, where the communications link is robust in the presence of EMI.